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High pH Levels

18th May 2021

High pH Levels

Regulating pH is one of the most important aspects of pool care and it should be maintained in the range 7.2 – 7.6.

High pH will also reduce the effectiveness of chlorine based sanitisers.

Probable causes

  1. Effect of mains water. The pH and alkalinity of your mains water will have a major influence on the water balance of the pool e.g. the pH, alkalinity etc. It is therefore important to regularly check both pH and alkalinity of the mains water when either refilling the pool or adding a substantial quantity of fresh water. Action can then be taken to make any necessary corrections to the pH and/or alkalinity. It is also important to regularly check the pH and alkalinity of the pool water. These two properties are closely linked, and a high pH can also mean there is a high alkalinity. A high alkalinity will make it difficult to lower the pH. To determine total alkalinity levels, use an alkalinity test kit or test strips.
  2. Effect of sanitiser. The sanitiser being used can have a significant effect on the pH. Of the chlorine based sanitisers in regular use, sodium hypochlorite (liquid chlorine) and calcium hypochlorite will tend to increase the pH. Sodium hypochlorite is strongly alkaline and will invariably require the use of a pH reducer. The effect that calcium hypochlorite has on the pH will depend on the make up of the mains water, i.e. whether the water is soft or hard.
  3. Excess use of pH increaser. It is important not to routinely add pH increaser without testing the pool water. Carry out regular tests and only add the quantities of chemical indicated by the test.

To reduce pH

  • Whatever the cause of high pH, it should be reduced to within the recommended range. To lower the pH, pH & Alkalinity Reducer at the recommended amount stated on the container. With the circulation running, distribute around the pool, avoiding the skimmers. Do not dose it in one spot otherwise some alkalinity may be destroyed.
  • If it is necessary to reduce both the pH and alkalinity, treat the alkalinity before the pH. To reduce the alkalinity, refer to below ‘pH Resistant to Movement’.

 

 

pH Resistant to Movement

This can cause cloudiness, excessive scaling and residues in the pool.

Probable cause – High total alkalinity

Total alkalinity is a measure of the alkaline materials (mainly bicarbonates) in the pool water and should be maintained in the range 80 – 150mg/l (ppm). Having sufficient total alkalinity prevents sudden pH fluctuation (‘bounce’) but an excessively high total alkalinity will make the pH resistant to change and the water will then become what is described as over buffered. High total alkalinity makes it difficult to adjust the pH as any correcting chemicals will have their effect taken up (buffered) by the total alkalinity. The management of pH will become relatively easy once the total alkalinity level is within the range of 80 – 150mg/l (ppm).

High total alkalinity can arise from a number of causes:

  • The make up (fresh mains) water has a high total alkalinity which is usually associated with a ‘hard’ water source, or the water supply company has artificially raised the alkalinity.
  • Overdosing with chemicals that are designed to increase the alkalinity.
  • Very high usage of sodium hypochlorite sanitiser (bleach/liquid chlorine) has on some occasions been associated with a high alkalinity.

To lower the total alkalinity

  • Carry out a total alkalinity test and if the reading is above 150mg/l (ppm), the level will need to be lowered. If you are unable to test for total alkalinity, take a fresh sample of pool water to your approved pool dealer who will carry out the test and advise on any necessary treatment.
  • To lower the total alkalinity, dose with Alkalinity Reducer at the recommended rate and should be repeated as necessary on a daily basis until the total alkalinity is below 150mg/l (ppm). With the circulation running, pour in a small area at the deep end of the pool, avoiding the skimmers.
  • Re-test the water after 24 hours and if the total alkalinity is still high, repeat the dose varying the location slightly but avoiding the skimmers.
  • Please note that the acid dosing technique is important here. To have the desired effect of reducing the total alkalinity rather than the pH, the acid must be poured into a small area of the pool and not widely dispersed. The aim is to create localised conditions of low pH such that the acidity will react with the bicarbonates which make up the bulk of the total alkalinity at normal swimming pool pH values.
  • If pH and total alkalinity both need correction, treat the total alkalinity first.